Zero KB ProRes 4444 export

I'm trying to export some keyed footage and retain the alpha, I have set the saver to quicktime .mov and choose Pro Res 4444 as the codec but each time I hit render the file has no data at all. I just get a Zero kb file every time. Does anybody know the answer to this problem?

Thanks in advance.

Same result here...

El Capitan has been causing 0kb renders in many applications. Have you recently upgraded?

10.11 issues aside, resolve doesn't support alpha out.